1. Field of the Invention
The present invention relates generally to a method and apparatus for mounting a rotary machine element, such as a drum pulley to a stationary shaft. More particularly, the invention relates to a novel technique permitting a pulley or similar element to be accurately positioned in a desired location along a stationary shaft and secured in the desired location without placing excessive and undesirable pre-loading on bearings supporting the pulley.
2. Description of the Related Art
Many applications exist in industrial, mining and other fields for pulleys mounted on stationary shafts. In many such applications, pulley wheels and idlers are mounted on machine frames, and belts, chains or other conveyor means are fed around the pulleys and idlers for moving raw and manufactured materials. In many conveyor systems of this type, drum pulleys are provided which offer excellent support for conveyor belts and contribute to maintaining proper alignment of the conveyor belts on the system components.
Many conveyor applications utilize several types of pulleys and idlers along an extended machine frame over which the conveyor belt runs. Certain of the pulleys may be provided on a "live" shaft. Such pulleys are generally fixed to the shaft and rotate with the shaft as the conveyor is driven. The shaft is, in turn, mounted on anti-friction bearings on the machine frame to permit free rotation of the shaft and pulley. Live shafts of this type are typically used to drive a conveyor belt or chain in the conveyor system. Other pulleys in the conveyor system may be mounted on "dead" shafts. Pulleys of this type will typically be mounted on a pair of bearing sets which are fixed at predetermined locations along the shaft. The shaft is then mounted by means of support blocks which prevent rotation of the shaft. The pulley rotates with respect to the shaft and machine frame, supported by the bearing sets, as the conveyor belt is drawn across it. Both live and dead shaft pulleys of this type are well known in the art and are commercially available from the Dodge Division of Reliance Electric Industrial Company.
Pulleys, idlers and other rotating drum-type elements configured for mounting on dead shafts generally include a central drum-like portion for supporting a belt or web, and end disks secured to the central portion. The end disks may be configured as annular disk-like elements or may includes spokes or recesses depending upon the weight and strength requirements of the application. The end disks are typically welded to the central portion to form a unitary structure.
Several arrangements and methods are known for attaching such rotary elements to dead shafts. In one known arrangement, a hub is precision machined along an interior annular surface and a bearing set is interference fit within the hub. The hub and bearing assembly are then fitted around the dead shaft and secured to the dead shaft to solidly fix the inner race of the bearing set to the dead shaft. An annular outer flange of the hub is then secured by means of bolts to a mating arrangement formed in the end disk of the pulley. In another known arrangement, regions of the dead shaft intended to receive the bearing sets are precision ground and the bearing sets are press fit into locations along the regions. In both arrangements, a first end of the dead shaft is relatively freely attached to the hub or bearing sets. However, as a hub or bearing set is secured to the second end disk of the pulley, the bearing sets are pre-loaded at one or both ends, resulting in undesirable stresses on the bearing elements and end disk attachment joints. Such pre-loading stresses can severely limit the useful life of the bearings and other system components.
In addition to undesirable pre-loading, known structures for mounting rotating members on dead shafts can be extremely difficult to disassemble for servicing of the bearings, shaft or rotating member. In particular, over time, components of the rotating machinery wear, or may fail, requiring removal of one or both bearing sets supporting the rotating member. However, in arrangements having bearing rings press fit to a dead shaft, disassembly requires that the rings be forceably drawn from the shaft, which may prove impossible without destroying the bearing or shaft, or both. Similarly, taper locking arrangements also are difficult to disassemble, requiring that a tapered locking sleeve be drawn from a mating hub.
There is a need, therefore, for an improved technique for mounting a pulley assembly or similar structure to a dead shaft, which avoids or reduces undesirable pre-loading of the support bearing sets between the pulley and the dead shaft. In particular, there is a need for an improved mounting system for dead shaft pulleys in which the pulley can be mounted at a desired position along the shaft and secured in place in a relatively straightforward manner. There is also a need for a dead shaft pulley mounting structure which is easy to assemble and disassemble for servicing of the pulley system components.